For several decades, MIL-STD-1553 has served as the workhorse networking standard for the integration of military/aerospace avionics platforms. MIL-STD-1553 's 1 Mb/s data rate and allowance for up to 31 remote terminals robustly supports traditional command and control applications for military avionics, and has served the industry well for many years. However, contemporary avionics applications result in increasing demand for network bandwidth and scalability beyond 1 Mb/s. In addition to command and control, these applications include processor and DSP clusters, digitized sensor interfacing, displays, file transfers, and data storage.
For new military aircraft, high-speed networking standards such as Fibre Channel, Gigabit Ethernet, and IEEE 1394 (FireWire) are being employed as a means of achieving higher data rates and wider connectivity. However, for the U.S. Department of Defense's (DoD's) large fleet of legacy aircraft, migration to newer networking standards necessitates extensive re-wiring of network cables and couplers, which generally entails a prohibitively high cost. As a result, there is a clear need to be able transmit higher data rates over the existing MIL-STD-1553 cable infrastructure.
By leveraging modern telecommunication modulation techniques, it is possible to transmit significantly higher data rates, on the order of hundreds of megahertz, over existing 1553 buses. Such methodologies are termed “Extended Bandwidth 1553” or “High Performance 1553” High Performance 1553. Hereafter, this document uses the designation “High Performance 1553.” While some subsystems will benefit greatly by migrating to higher data rates, there will also be many other subsystems on existing 1553 buses that do not require higher bandwidth. These systems will need to continue using 1 Mb/s MIL-STD-1553 signaling, while co-existing with the higher speed traffic on the same buses.
In order to transmit higher data rates over legacy MIL-STD-1553 cable plants, a number of issues need to be addressed. These include channel bandwidth capacity, electromagnetic interference (EMI) constraints, noise, and the presence of 1 Mb/s MIL-STD-1553 signals. Channel capacity is the result of bandwidth limitations of legacy 1553 cables, stubs, and couplers. Signal level limitations are the result of MIL-STD-461 EMI constraints; the presence of 1 Mb/s 1553 signals compounds this by further reducing the allowable High Performance 1553 signal level. Sources of noise include transmitters and receivers connected to a multi-drop 1553 bus, as well as conducted and radiated transients from various external sources.
This invention deals with embodiments of two different methodologies for receiving High Performance 1553 signals in the presence of concurrent 1 Mb/s MIL-STD-1553 signals being transmitted over the same data bus. The problem encountered results from the fact that the frequency spectrum for legacy MIL-STD-1553 signals extends significantly beyond the fundamental frequency of 1 MHz. There are multiple approaches for dealing with this problem, with each having with its advantages and disadvantages. Four possible approaches include:
As a means of limiting harmonic content above 1 MHz, low pass filters are installed in-line with all legacy 1553 transmitters. However, there are significant cost and logistics issues associated with this proposed implementation.
Positioning the High Performance 1553 signal bandwidth to a frequency band above which there is no significant MIL-STD-1553 signal content. A drawback of this approach is that precludes a major portion of spectrum which has relatively strong channel response for use by High Performance 1553 signals.
The High Performance 1553 signal may be transmitted over the redundant bus; i.e., the bus that is not currently being used by legacy 1553 signals. However, this technique may result in degraded performance if one of the dual redundant buses fails.
A predictive cancellation methodology for receiving High Performance 1553 signals in the presence of concurrent MIL-STD-1553 signals. The goal of the cancellation is to remove the 1 Mb/s MIL-STD-1553 signal from the composite input signal. Predictive cancellation allows for reception of High Performance 1553 signals with concurrent MIL-STD-1553 signals, without necessitating the sacrifice of significant amounts of High Performance 1553 signal bandwidth.